Method of preparation of metal salts



United States Patent 2,716,588 METHOD or PREPARATION or- METAL SALTSJames 1). Hall, Shaker Heights, Ohio No Drawing. Application October 8,1954,

Serial No. 461,296

32 Claims. (Cl. 23-425) The present invention relates generally to metalcorrosion and the preparation of metal compounds and is moreparticularly concerned with a ,novel and very economical and usefulmethod of preparing metal derivatives such as salts and sulfides, andwith a method of separating the metal values of alloys rapidly,economically and very sharply.

The chemical art has long been concerned with the problem of metalcorrosion and substantial progress has been made in the application ofcertain very corrosionresistant metals, such as nickel, and in thedevelopment 2,716,588 Patented Aug. 30, 1955 special utility in respectto this latter situation, particularly where it is desired to producedirectly, rapidly, economically and commercially a salt of such metalmade from a weaker acid.

In the case of Monel metal, again, the production of nickel and coppercompounds therefrom has always been a slow and expensive operation andof no commercial significance because of this and because of the addeddifliculty of making a good separation of the compounds obtained. Oneprior art procedure, which to the best of my knowledge has never enjoyedcommercial success to any extent, although patented by a large chemicalmanu facturing concern, involves subjecting a mixture of finely dividedMonel metal andwater to the action of sulphur dioxide under elevatedtemperature and pressure conditions. Under high pressures, such as topounds per square inch gauge, appreciable corrosion of the alloy andproduction of nickel sulphate and copper sulphate results in accordancewith this method. Nevertheless, the rate of corrosion obtained is notsufiiciently rapid to make the process attractive commercially,particularly since a special nickel sulphate-copper sulphate separationoperation must be carried out after the corrosion step is finished, andthis operation involves conversion of the copper sulphate to coppersulphide and a subsequent slow filtering step. Moreover, the use ofpressure entails a substantial initial expense for special equipment.

According to another Monel conversion process, which incidentally hasalso been patented by the company re ferred to above and has not beenpracticed commercially,

the alloy is subjected to the action of dilute sulphuric acid whichnickel tends to dissolve and the excessive cost in time involved in suchproduction due to nickel passivity. Thus, in accordance with oneparticular procedure which has been attempted in various forms, manytimes nickel is contacted with concentrated sulphuric acid (50% byweight) and at first begins to corrode at a reasonably good rateproducing nickel sulphate. However, before the reaction proceeds to thepoint where substantial corrosion is effected, the reaction slows downpractically to a standstill due to the hydrogen over-voltage developedon the surface of the nickel. The resulting passivating elfect on thenickel body is virtually complete and no matter how much the acidconcentration is. increased,'the corrosion rate is not materiallyafiected. No known means, chemical or physical, has hitherto beenconsistently capable of relieving this condition although \u'rtuallyeverything has been tried. Thus, efiorts to operate under hightemperature or high pressure circumstances have failed insofar as theirobject has been to relieve the passivity of the nickel.

Similar problems andfllifliculties present themselves when an attempt ismade to produce salts of nickel other than the sulphate or the chlorideor to produce salts of metals other than nickel, starting with the metalin its elemental form. Nickel, for instance, is corrodable in accordancewith the best prior art practices using, for example, acetic acid, atonly a very slow and completely unsatisfactory rate, regardless of thetemperature, pressure, acid concentration or other physical orphysicalchemical or chemical circumstances. Other metals classed withnickel and copper as corrosion resistant because of thesecharacteristics include aluminum, cobalt, zinc, cadmium, chromium, lead,antimony, tin, iron and molybdenum. It will, therefore, be understoodthat while a given metal may present no substantial corrosion resistanceto certain acids, it may be quite resistant to attack by other acids,and that the present invention process has under conditions of anabnormal concentration or partial pressureof oxygen and an elevatedtemperature such as about to C. If the air used is not under pressure,free oxygen must be added to the air to produce the stated results. andsuper-atmospheric pressure are employed together, the rate of corrosionof the alloy is so slow that this method is impracticable particularlyin view of the substantial additional time and expense involved inseparating the sulfate reaction product of nickel and copper, asindicated above. The additional expense which the use of pressure and/oroxygen in this manner would entail, makes the process even less feasibleeconomically.

In accordance with my present invention, which is based upon mysurprising discoveries subsequently to be described, it is possible, forthe first time to my knowledge, to increase materially the rate ofcorrosion of metals and alloys such as those mentioned above, and at thesame time to produce derivatives of these metals and alloys which may berapidly and easily separated. Thus, for instance, nickel and copper inthe form of Monel metal or as individual elements can be charged into areaction vessel and converted in accordance with this invention, thenickel salt resulting being soluble and going into solution in thereaction mixture, while the copper derivative is produced as a solidwhich accumulates on the bottom of the vessel as an easily filterablesludge-like material. This isa very practical and economical method andat the present time is being applied commercially successfully to nickeland to Monel metal in relatively smallscale operations but at a highmargin of profit, compared to any and all prior art Monel conversionproc esses. It is also possible, according to my invention, to preparerapidly and economically metal compounds from other metal values. Forexample, nickel sulphate can be made from nickel sulphide-coppersulphide by subjecting the mixed sulphides to the action of sulphurdioxide in an aqueous sulphuric acid solution.

Failure of the prior art in this connection and the success of thispresent process is attributable entirely to my aforesaid discoveries abasic one of which, briefly stated,

In any event, even though free oxygen' is that sulphur dioxide underspecial circumstances will function very effectively and rapidly toconvert normally very corrosion-resistant metals and metal alloys intometal compounds, such as salts and sulphides. The reactions involvedtake place almost instantaneously where conditions are proper andaccordingly the process may be carried out in liquid media which arepractically at their boiling point temperatures and in which theconcentration of sulphur dioxide at any given time can thus not possiblybe substantial. I have further discovered that where a metal standsabove hydrogen in the electromotive force series, the use of sulphurdioxide in a particular manner will result in the rapid corrosion of themetal and the production of the salt of the metal of the acid present inthe reaction mixture. Still further, I have found that where the metalinvolved stands below hydrogen in the said series, the corrosion of themetal carries forward at a similarly rapid rate with the result that thesulphide of the metal is produced. Generally, therefore, the corrosionin accordance with this process of the metal above hydrogen results inproduction of a salt solution of that metal, while the corrosion of themetal below hydrogen results in the production of the sulphide of thatmetal which normally will be insoluble in the reaction solution and willaccumulate as a sludge-like deposit on the bottom of the reactionvessel. I have additionally discovered that metals behave according tothe foregoing rules when they are delivered into the reaction mixturesof this invention in alloy form. Thus, where an alloy contains orconsists of a metal above hydrogen and a metal below hydrogen in thesaid series, the use of sulphur dioxide in a particular manner willresult in the rapid production of a salt of the higher standing metal,and in the simultaneous production at the same rate of the sulphide ofthe metal below hydrogen. found that where an alloy contains or consistsof two metals, both of which are above hydrogen, the salt of each of themetals will be produced. On the other hand, where the alloy contains orconsists of two metals, both of which stand below hydrogen in saidseries, the sulphides of these metals will be produced.

In producing the foregoing results in the process of my invention,sulphur dioxide behaves in a novel and hitherto unknown manner. Thus,instead of being oxidized with resulting production of sulphate radical,the sulphur dioxide is reduced through the reactions of this process sothat elemental sulphur is formed and precipitated from the liquid phaseof the reaction mixture of this sulphur dioxide sulphur is convertedinto a sulphide compound. Elemental sulphur results as an end productwhere there is no metal below hydrogen available in the reaction mixturefor sulphide production.

Very generally, the method of this invention comprises the step oftreating a metal with sulphur dioxide in an aqueous solution containingmore than about 0.5% by weight of a strong acid selected from the groupconsisting of formic acid, acetic acid, sulphuric acid, hydrochloricacid, hydrofluoric acid, nitric acid and phosphoric acid.

Preferably, the metal is in comminuted form in order that the surfacethereof available for corrosion will be at a maximum for greatestproduction and efliciency. The temperature of the mixture is, for thesame reason and purpose, maintained relatively high throughout theprocess even though appreciable corrosion of the metal may be realizedat room temperature, i. e. about 65 to 70 F. Temperatures in the rangebetween about 80 C. to about 100 C. or higher up to the boiling pointtemperature of a given reaction mixture under atmospheric pressure, willhowever, generally be found to produce the best results from thestandpoint, at least, of corrosion reaction rates. Air can be, to thissame general purpose, bubbled into the solution while the process isgoing on, since the agitating effect thereby obtained in the solutionassures clean metal surfaces for reaction and substantial uniformity ofacid concentration throughout the solution.

Further, I have Cit In general, any gas or mixture of gases not having adeleterious etfect on the process may be used to accomplish thisagitation to advantage, but air will normally be preferred for reasonsof economy and also because of its free oxygen content to which, Ibelieve, certain advantages in the preferred practice of this inventionsubsequently to be described, are attributable.

Pressure is not necessary to the practical and commercial operation ofthis process and, in fact, has relatively little effect upon the courseof the corrosion re actions, even though it may enable the applicationof somewhat higher temperatures to the reaction mixture, andsuper-atmospheric pressure is accordingly not preferred in the bestpractice of the invention. Sub-atmospheric pressures result indepression of boiling point temperatures and to this extent, at least,are not prefer-red for use in the present process.

The acids suitable for use in the process include those which aresubstantially completely soluble in water (without substantialdecomposition), i. e. to an extentgreater than about 80% on the basis ofthe volume of water employed. These acids also have other properties incommon, namely a relatively high ionization potential and substantialstability against'the decomposing effects of heat up to approximatelythe boiling point temperatures of the present reaction mixtures undersubstantially atmospheric pressure. Thus, these acids are quiteeffective in dilute aqueous solution and exert their effects noticeablyeven in relatively very small concentrations, such as down to about0.5%. I have found, however, that the foregoing novel results andadvantages of this invention cannot be obtained where the concentrationof acid in the reaction mixtureis less than about 0.5% at the beginningof the reaction period or for the greater proportion of that period;This is due to the fact that the unique sulphur dioxide reaction of thisinvention apparently does not take place when the concentration of acidis below that minimum value.

The acids specified above may be used singly or in any desiredcombination with the understanding however, that certain of them will beincompatable such as nitric acid and formic acid or acetic acid, andthat it would not ordinarily serve any useful purpose to combine suchacids in a single medium. Theacid concentration, whether one or moreacids are used, should not be maintained any lower than the minimumstated above because the process and the metal corrosion reactionsinvolved therein will then proceed too slowly for practical purposes. Itwill be understood, therefore, that the acid concentration cf a solutionfor use in this process should initially be substantially in excess of0.5%, but that it may be approximately 0.5% and' be maintained atsubstantially that value. In the absence of detectable (by standardsensitive acid determination techniques) amounts of acid in thesolutions employed in this process, the reactions and results of thisinvention are apparently not affected or obtained. In practice, I preferto maintain the acid concentration above about 2% by weight throughoutthe major portion of the reaction (corrosion) period, and I have foundthat better results are to be obtained where this concentration is stillhigher, as above about 5% to 10%. As long as there is some waterpresent, the process may be carried out with the foregoing results andconsequently no maximum limit need be fixed on the concentration of theacid r in the solution. As a practical matter, however, a concentrationof 50% to 60% of sulphuric acid will be found a reasonable maximum foreither initial or maintained concentrations inasmuch as results obtainedabove this level will not ordinarily be sufficiently improved to justifythe greater expense involved in the use of excessive amounts of acid.

As used herein, the term corrosion means and refers to chemical, ratherthan physical, conversion of a substance. Thus, in accordance with myusage of the term, corrosion defines the action involved in making ametal compound, such as a salt or a sulphide, from a metal in elementalform.

From the foregoing, it will be understood that an alloy of two or moremetals may be used, rather than a single metal, in which case aplurality of metal compounds will be produced. These compounds will besalts or sulphides of the metals used, depending upon the position ofthese metals with respect to hydrogen in the electromotive force series.The rule stated above governing this matter of metal products isapplicable fully regardless of what metals or combinations of alloysthereof are employed as starting materials, and regardless of which ofthe specified acids or combinations thereof are employed in the reactionmixture. Thus, the metals in an alloy of four or five constituents,which has hitherto withstood all efforts to separate and recovereconomically the values therein can be treated successfully inaccordance with this invention and at the outset of my process aseparation between the metals above and below hydrogen will be obtainedas the corrosion reactions go on.

The expressions above hydrogen in the electromotive force series andbelow hydrogen in the electromotive force series, are employed hereinand in the appended claims in accordance with general usage andunderstanding in the art. Thus, the first expression identifies a metalwhich is electronegative with respect to hydrogen, such as nickel orchromium, and the second expression identifies a metal which iselectropositive with respect to hydrogen, or in other words, a metalsuch as mercury or copper.

There is, among those skilled in the art, some doubt and disagreement asto the proper positions of some elements in the electromotive forceseries. For the purpose of this invention and specification, however,the table set out on page I380 of Handbook of Chemistry and Physics(28th edition) by Charles D. Hodgman (published by Chemical RubberPublishing Co.), may be consulted in determining the relative positionof a given metal element with respect to hydrogen in the said series.

The metals and alloys which are especially suited for use in thisprocess are those relatively corrosion resistant metals and alloys, suchas aluminum, nickel, cobalt, zinc, cadmium, chromium, lead, antimony,tin, iron, copper, molybdenum, nickel alloys like Monel metal andChromel, copper alloys including copper-mercury amalgams, cobalt-copperalloys, cobalt-arsenic alloys, brasses and bronzes. The method of thisinvention, however, is not limited to use with or on these particularmaterials, but may be applied more generally to mixtures of two or moreof. these metals and alloys, as well as to other less common corrosionresistant metals and alloys to produce metal or alloy corrosioncompoundsof metals including sulphides and salts. Silver and silver alloys arerepresentative of the latter category but, at the same time, silverstands here as an exception in that I not only do not recommend theapplication of this process to the noble metals but also that] expresslyexclude from all the appended claims all noble metals. It will,therefore, be understood, that I do not contemplate the use of theprocess of this invention on any noble metal except silver or on anymetal with any acid which readily or continuously attacks that metal. Asthose skilled in the art well know, the alkali metals are readilycorroded by water alone and, much more readily by all acid solutions;and iron, aluminum and zinc are readily and continuously corroded byhydrochloric, sulphuric, nitric and hydrofluoric acids, but not byacetic, formic and phosphoric acids. It is also well known thatchromium, lead, nickel, cobalt, antimony, tin, cadmium, and molybdenumare quite resistant to corrosion by hydrochloric, sulphuric, nitric andhydrofluoric acids and are even more resistant to corrosion by acetic,formic and phosphoric acids. It is also well known that copper is quiteresistant to corrosion by hydrochloric, hydrofluoric, acetic, formic andphosphoric acids, but is readily corroded by sulphuric and nitric acids.

It is also well known that metals which are readily corroded by certainacids are quite resistant to those acids when alloyed with other metals.For example, iron, which is readily attacked by sulphuric acid, becomesvery resistant to corrosion by that acid when alloyed with nickel andchromium to form stainless steel; also copper, which is readily corrodedby sulphuric acid, becomes quite resistant to corrosion when alloyedwith nickel to constitute Monel metal.

Accordingly, the expression normally very resistant to corrosion, asused in this specification and particularly in some of the appendedclaims, is intended to exclude from the scope of the claims in which itappears all metals and alloys which, when treated with a particularacid, are readily and continuously corrodable by that acid; and toinclude within the scope of the claims in which the aforesaid expressionappears those metals and alloys which, when treated with a particularacid, are not readily corrodable. As a specific illustration, thisexpression excludes from the claims in which it appears iron whentreated with any of the above-mentioned inorganic acids; but includesiron when treated with any of the foregoing organic acids. It willtherefore be understood that I do not contemplate the use of the processof this invention on (1) alkali metals and similar metals and alloys;(2) and all of the noble metals except silver; and (.3) iron, steel,aluminum and zinc which exhibit no substantion resistance to corrosiveattack when used with solutions of hydrochloric, sulfuric, nitric andhydrofluoric acid. These metals and alloys of (l) and (2) are expresslyentirely excluded while the metals of (3) are expressly excluded whenused with the specified mineral acids, from the appended claims by theexpression corrosion resistant.

As indicated above, however, the present method may be successfullyapplied to metal compounds to convert them into other compounds whichmay be desired as end products or as a means for accomplishing an easyand economical separation of various metal values, as will subsequentlybe described in more detail.

The acid selected for use in the process should be one which willproduce the desired salt of the metal employed. For instance, wherenickel sulphate is desired as a reaction product, sulphuric acid shouldbe used and no hydrochloric acid or other acid, which could interferewith the desired reaction, should be present in the reaction mixture.Similarly, if nickel chloride is desired, hydrochloric acid should bethe only effective acid present in the reaction mixture. A mixture ofnickel salts such as sulphate or chloride may be produced in the sameoperation and simultaneously, in accordance with this invention, where amixture of acids is present in the reaction mixture during the corrosionphase of the process. Where a metal sulphide rather than a metal salt(in the sense that the term salt has been used above and in the appendedclaims) is to be produced, as in the case of treatment of thecopper-mercury amalgams, the acid used may be any one or more of thosedisclosed above, the initial concentration of the acid being theimportant consideration in such case, assuming other factors such astemperature and pressure to be constant.

As applied to a physical mixture of nickel and copper or to Monel metalon a commercial scale, my process is suitably carried out in alead-lined receptacle and the metal in comminuted forms such asturnings, clippings, stampings, wire, screen, etc., is introduced into asolution of water and sulphuric acid contained in the vessel. A largeproportion of metal surface for reaction is thereby provided and thecorroding action of the solution approaches the theoretical maximumeifectiveness. The acid which I have employed with consistent success isconcentrated commercial sulphuric acid 1.83 specific gravity and I haveincorporated it in the proportion of 45% by weight of such acid towater, the proportion of the metal or alloy by weight to the acid andwater solution being approximately 20% to 50%.

a The reaction vessel is equipped with steam coil heating means and thereaction mixture, comprising the acidic solution and the comminutedmetal, is maintained at approximately the boiling point temperature ofthe solution, this temperature varying somewhat as the amount of nickelsalt dissolved therein varies as the corrosion reaction progresses.

I have found that a very rapid rate of corrosion is realized by addingto the water, at the beginning of the operation, two-thirds of the 45%proportion by weight of concentrated sulphuric acid, or 30% by Weight ofsuch acid to water, and by adding the additional 15% by weight to theboiling solution when the proportion of sulphuric acid therein has beenreduced to approximately 15%, which addition will bring the proportion,of acid to the solution to its original proportion of 30% by weight, itbeing noted further that additional water will be added to the solutionto maintain the volume of the latter substantially constant despite theloss by evaporation due to boiling. Because of the fact that the 30% byweight of sulphuric acid is incorporated in a solution which ismaintained at boiling point, there will be no danger that the acid willproduce more nickel sulphate by its reaction on the nickel of the alloythan can be held in solution while the latter is hot.

During the boiling operation, the reaction mixture is kept saturatedwith sulphur dioxide, or a suitable solution of the same, by causing thegas or solution to be introduced in such manner as to distribute it aswidely and as intimately as possible in contact with the metal or alloy.

Owing to the fact that the sulphur dioxide cannot remain long in theboiling reaction mixture into which it is introduced, its reaction uponthe copper of the metal mixture or alloy must be practicallyinstantaneous, and therefor its supply to the bath must be ample andconstantly maintained; in fact, it will be difiicult to supply moresulphur dioxide than adequate to form copper sulphide with the copperconstituent of the nickel-copper mixture or alloy.

Although my process will proceed without air being present in or incontact with the reaction mixture, I have found it advisable to supplyair to the said mixture in a controlled amount, at a controlledvelocity, and in a manner which will enable the air to be distributed asintimately as possible through the mixture for intimate contact with themetal or alloy.

The air employed in this manner functions, I believe to keep thesurfaces of the alloy particles swept substantially clean ofaccumulations of reaction products,

particularly the solid phase products, and assists in agitating thereaction mixture to maintain a substantially uniform acid concentrationthroughout said mixture. Also, I believe that the oxygen in the airaugments that derived by analysis of the sulphur dioxide in the reactionmixture and reacts with nickel of the metal mixture or alloy formingnickel oxide as an in termediate product, which is almost immediatelyconverted to nickel sulphate upon hydrolysis and reaction with thesulphuric acid in the solution. Care, however, should be exercised inthe use of air in the reaction mixture in this manner because it ispossible to oxidize copper sulphide to copper sulphate and as soon ascopper sulphate appears in any detectable amount in the reactionmixture, the corrosion reactions materially abate or cease, apparentlybecause of catalytic poisoning, the mixture of metals or the Monel metalpresumably exerting a catalytic effect on the analysis of the sulphurdioxide in the acidic reaction solution. The rate at which air isdelivered into and through the reaction mixture consequently should becontrolled to avoid the formation of copper sulphate in this manner.Different equipment will require different air-flow conditions, andtemperature will also have an effect upon fixing maximum air tolerance.Therefore, routine experiments should be carried out to determinesuitable or optimum conditions before new equipment or new reactionmixtures are put into full scale commercial use. in the event thatcopper sulphate is formed, the air supply should be temporarily shut offand the reaction mixture stagnated until the copper sulphatedeteriorates to the sulphide. Alternatively, the mixture may be gassedthoroughly with hydrogen sulphide to effect conversion of the coppersulphate to copper sulphide, whereupon the metal or alloy corrosionreactions may again proceed and air may be introduced into the mixturein a limited quantity.

The foregoing treatment should be continued until the sulphuric acid inthe reaction mixture shall have been exhausted or substantiallyexhausted, the time required for such treatment having been found by meto approximate sixteen hours in the better commercial practice of thisinvention. When the sulphuric acid in the mixture shall have been soexhausted, the supply of sulphur dioxide and air should be turned offand the mixture be allowed to continue to boil to expel any sulphurdioxide that may remain therein. The mixture is then filtered and theprecipitate of copper sulphide is washed thoroughly and set aside forthe preparation therefrom of metallic copper or desirable copperchemicals. The filtrate (mainly nickel sulphate), which is slightlyacidic, can be treated with hydrogen sulphide to precipitate therefromany copper that may be therein as copper sulphate, or it can be passedover nickel turnings, thereby to cement out the copper. The filtratewill be thus purified of any tramp copper, i. e. copper values picked upas an impurity from equipment during handling. 7

The filtrate, which consists essentially of nickel sulphate, may, ifdesirable, be subjected to any of the well known treatments whereby itwill be converted into other nickel salts; or metallic nickel may berecovered therefrom by any of the well known processes.

By the use of sulphur dioxide in the above-described process, I amenabled to sulphide the copper constituents of the nickel-coppermixtures or alloys and thereby make the production of copper sulphide,and the recovery of copper or the production of other copper compoundstherefrom, a commercially profitable proposition while at the same timeaccomplishing the recovery of nickel sulphate from said mixtures oralloys.

The variations in proportions of the acid and water solution to metal oralloy as given hereinbefore are based upon the assumption that the metalor alloy is placed within a receptacle in a divided or discretecondition. However, if the metal or alloy is in the form of largemasses, such as bars and plates, obviously the proportion of the acidandwater solution to metal or alloy should be correspondingly increased;and where the process is carried on in a reaction tower wherein the acidand water solution flows over the metal or alloy, a still greaterproportion of acid and water solution to metal or alloy should beemployed and in such application of my process I would preferably employa constant 30% by weight to water solution of acid.

I am aware that a number of processes have been evolved for the recoveryof nickel from nickel-copper alloy waste or scrap but, so far I amadvised, none of these processes has gone into extensive commercial use,principally because of their prohibitive cost. By the process set forthherein, both nickel and copper and or their salts can be separated fromnickel-copper alloys and at a cost which renders the process capable ofcommercial adoption.

I have also found that my process, as set forth at length hereinbefore,can be advantageously employed for the production of nickel sulphatefrom metallic nickel and will greatly reduce the time which has beenrequisite heretofore for the corrosion of the nickel and the productiontherefrom of nickel sulphate.

In carrying out this process separately on cobalt or brass rather thannickel or Monel metal, Iv have successfully followed the procedureoutlined above, using cobalt or brass turnings and emplc ing a sulphuricacid solution to make up the reaction mixture with the turnings, theconcentration of the acid amounting to about 45% by Weight as before.The proportion of cobalt or brass to the acid and water solutionamounted to about 40% by weight at the beginning of the reaction.Sulphur dioxide gas was introduced into the lower portion of thereaction vessel: well beneath the surface of the mix= ture at the sametime that steam was introduced into the steam coils. of the lead-linedvessel. The corrosion reactions began immediately thereafter andincreased in rate up to the time that the boiling point temperature ofthe resulting mixture was reached. As before, no attempt wasmade tomaintain super-atmospheric pressure on the reaction mixture. Rather thereaction vessel was left open and the fumes evolved from the mixturewere vented through a stack opentothe atmosphere. Air was introducedintothe reaction mixture under controlled circumstances, as describedabove, beginning at approximabely the same time that the sulphur dioxideflow was started andv continuing throughout the reaction period.

When the concentration of the sulphuric acid in the reaction mixturediminished to about 30% by weight of the acid to the cobalt sulphate orthe zinc sulphate solution, an additional- 1-5% by weight of theconcentrated acid of 1.83 specific gravity was added. No furtheradditions of acid were made and the heating and gassing of the reactionmixture was continued until the cobalt or brass and acid therein: werevirtually exhausted. A total of 16 hours was required to carry thecorrosion reactions to completion whereupon residual sulphur dioxide ofthe mixture, after the supply ofgas to the mixture has been cut off, wasboiled out and the elemental sulphur was separated from the mixtureconsisting, primarily of. cobalt sulphate and water in any suitablemanner. Where brass instead of cobalt was used the mixture was filtered,following boiling to expel residual sulphur dioxide, and the coppersulphide was thoroughly washed, while the filtrate consisting primarilyof zinc sulphate and water is collected for further treatment.

I- have also successfully treated finely-divided, chromium in the mannerdescribed above, a phosphoric acid solution being employed with theobject of producing a chromium phosphate solution. The starting solutionwas prepared by adding 125 cc. of 85% orthophosphoric acid to 250. cc.of water. The chromium. particles were introduced into the solution andthe sulphur dioxide gas and air were delivered in equal volumes into themixture as described above. A few moments later, heat was applied to themixture by means of steam coils and the heating was continued until thetemperature of the mixture had reached 90 C., and flow of air andsulphur dioxide was continued until the chromium was virtually exhaustedat the end of about 7 hours. The reaction mixture was subjected to.-atmospheric pressure through out the reaction period. The elementalsulphur in the solution was separated and removed from the liquid phaseof the mixture which contained substantial quantitiesof chromiumphosphate.

I have also successfully treated Chromel. Wire in the manner generallydescribed above,.a sulphuric acid solution being used as the startingsolution. A total of only 2 hourswas required for complete conversion ofmetal values in one of these Chromel treatments where. only 82.5 gramsof' fine standard Chromel wire was used. The temperature of the reactionmixture at the beginning of the process, when the sulphur dioxide andair was introduced into the mixture, was approximately 95 C. and thepressure of the mixture was approximately atmospheric.

In some small scale operations I have determined the suitability ofstill other metals, alloys and acids. Inone particular trial, I prepareda mixture consisting of 400 grams of Monel turnings, 1 50" cc. ofcommercial acetic acid (glacial of about strength) and 250 cc. of water.With the mixture under atmospheric pressure and at about 85 C., Iintroduced sulphur dixoide thereinto' at the rate of about one bubbleper second, and introduced air thereinto at about one-half that rate.The corrosion and conversion of the Monel metal was complete at the endof 2 hours. Nickel acetate and copper sulphide were the reactionproducts, all the nickel acetate being dissolved in the reaction mixtureand all the copper sulphide being in the solid phase as aslud'gelikemass on the bottom of the reaction vessel.

Using a commercial hydrochloric acid of about 28% strength, I havesuccessfully practiced the process of this invention by making areaction mixture of this acid and about four times its volume of purewater, and adding thereto Monel metal turnings. The volume of thereaction mixture and the amount of Monel metal approximated that statedin the above acetic acid example. With the reaction mixture atapproximately C., sulphur dioxide was introduced into the mixture andwithin about 2% hours corrosion of the Monel metal was complete and theentire nickel value thereof was contained inthe liquid. phase of thereaction mixture as nickel chloride, while substantially all the copperthereof existed as copper sulphide sludge.

ln another relatively small scale operation, I successfully tested thesuitability of'nitric' acid in this process,

cadmium. metali being used in. one test and Mon'el metal.

being used in another test. In each case approximately 400 grams ofmetal. were used and the nitric acid was diluted to about25% strength.to make up the reaction Sulphur dioxide and air were again delivered.

mixture. intov the' mixture continuously, resulting in the formation ofcadmium nitrate and elemental sulphur in one instance andcopper sulphideand nickel nitrate in the other, the said nitrates being dissolved inthe liquid phase of the reaction mixture, thus enabling easy and sharpseparationt of the metal values. Unlike the previous examples-v in thiscase, the reaction mixture was maintained at about roomtemperature, i.e. about 20 C. to about 30 C. throughout the reaction period.

To determine further the effectiveness of phosphoric acid in the-processof this invention, ladded 125 cc. of

85% orthophosphoric acid to2'50 cc. of water, introduced. intotheresulting solution 400 grams Monel metal turnings, and thenpromptlyturned sulphur dioxide gas and air in equal volumes into the mixture.Seven minutes later, heat was appliedto-the mixture by means of steamcoils inthe reaction vessel and the liquid phase of the mixture by thistime has turned milky. When thesolution temperature reached 42 C. ittook on a greenish color. The heating was continued until thetemperature of the mixture reached 98 C. After one hour, during whichthe temperature was maintained substantially constant at 98' C. andgassing with sulphur dioxide and air was continued, the supply ofsulphur dioxide and air to the mixture' was cut offand I determined that40% of the original acid content of the mixture was exhausted.

I then filtered the solution, boiled the filtrate to expel the sulphurdioxide, and tested the filtrate for copper, finding that it containednone. A test of the filtrate for sul phate formation also provednegative. The nickel phosphate product, being soluble in aqueous acids,was contained in substantialquantity in solution in thefiltratezbecauseof the presence of free phosphoric acid therein.

In another set of experimental operations, I mixed in. two batches cc.of 50% hydrofluoric acid with 280 cc. of water and to one batch I added400 grams of cobalt scrap and to the other batch I added 400 grams ofMonel metal turnings. Sulphur dioxide gas and air were turned into theresulting mixture promptly thereafter and heat was appliedthereto, asdescribed above, beginning five minutes after the gassing was started.The solution in contact with the cobalt scrap was milk-y throughoutsubstantially the entire reaction period of one hour and the temperaturethereof was maintained between 75 and 90 C. during this time. Thetemper.- ture of the cobalt reaction medium was maintained between aboutC. and about C. throughout the re action period. When the gassing of theMonel metal mixture was discontinued at the end of the hour, Idetermined that two-thirds of the hydrofluoric acid had been consumedand on testing the liquid phase of the reaction mixture for copper, Ifound none. A test for sulphate formation on the liquid phase of thisMonel metal reaction mixture also proved negative. A similar test forsulphates on the cobalt scrap mixture proved negative and it was foundthat the cobalt fluoride in solution was stoichiometrically equivalentto the cobalt scrap consumed in the process.

Formic acid was tested in the same general manner, 150 cc. of 90% formicacid being added to and mixed with 250 cc. of water, and 400 grams ofMonel turnings being introduced into the solution, gassing of theresulting mixture with sulphur dioxide and air in equal volumes beingbegun immediately thereafter. The temperature of the mixture during thereaction period of about one hour was maintained about C., during whichtime approximately one-half of the original acid content of the mixturewas consumed. A test of the liquid phase of the final mixture for copperand another test thereof for sulphate formation proved negative. Thenickel formate product was contained in solution in liquid phase of themixture.

In a parallel experiment wherein the same reagents and conditions wereemployed, except that nickel was used instead of Monel metal, similarresults were obtained. The nickel formate product proved to be free fromsulphate contamination and was distributed between the liquid and thesolid phase due to its limited solubility.

'In still another small scale operation, I prepared a mixture consistingof 400 grams of zinc turnings, 150 cc. of commercial acetic acid(glacial of about strength) and 200 cc. of water. With the reactionmixture under atmospheric pressure and at about 85 C., I introducedsulphur dioxide thereinto at the rate of about one bubble per second andI introduced air thereinto at about one-half that rate. The corrosionand conversion of the zinc was visibly rapid and was virtually completewithin about two and one-half hours. The zinc acetate in solution in thereaction mixture was the primary reaction product although a certainamount of finely-divided sulphur in sludge-like form collected on thebottom of the reaction vessel when the mixture was permitted to stand.

I similarly tested the conversion of iron to produce iron acetate inaccordance with this invention process, using 400 grams of ironturnings, 150 cc. of commercial acetic acid and 250 cc. of water, asstated in the foregoing example. The introduction of sulphur dioxide andair in the reaction mixture was carried out as specified immediatelyabove and the results were virtually the same in that reaction wascomplete at the end of about four and one-half hours. The iron acetateproduct was contained in the reaction solution while a semi-colloidalsulphur sludge was accumulated on the bottom of the vessel.

In still another experimental run, I introduced finelydivided nickelinto a solution of hydrochloric acid of about 28% strength, diluted toabout four times its volume with pure water. Sulphur dioxide gas and airwere turned into the mixture and heat was applied to it as describedabove, beginning about five minutes after the gassing was started. Thetemperature of the solution was maintained between about 75 C. and 90 C.throughout the reaction period. The gassing of the mixture wasdiscontinued on substantial exhausion of the metallic nickel. The amountof nickel chloride contained in solution in the reaction mixture provedto be stoichiometrically equivalent to the amount of nickel charged tothe vessel and reacted therein. The solid phase of the reaction mixture.consisted essentially of semi-colloidal sulphur which collected on thebottom of the reaction vessel and was readily separated from the liquidportion of the said mixture.

To study the efiects of pressure of the present process, I prepared areaction mixture of about 250 grams of Monel metal, 40 cc. sulphuricacid (commercial 1.83 specific gravity) and 210 cc. of pure water. Witha pressure of 30 pounds per square inch gauge, on the reaction mixtureand the temperature of the mixture at 85 C., I introduced air andsulphur dioxide gas into the mixture at the same rates and in equalvolumes for a period of three hours. At the end of this time, corrosionof the Monel metal was essentially complete and the metal values thereofexisted as nickel sulphate in solution and copper sulphide in sludgeform.

In an experiment carried out upon a complex alloy, the objects andadvantages of this invention as set forth above were fully realized. Thealloy employed contained in substantial amounts, copper, lead, tin,zinc, silver, and iron and was one which hitherto has resisted allefforts to obtain rapid corrosion and subsequent easy and sharpseparation of its metal values. The reaction mixture employed consistedessentially of 400 grams of this alloy dispersed in a solution of 60 cc.of sulphuric acid (commercial 1.83 specific gravity) in 315 cc. ofwater. With the temperature of the reaction mixture at about C. and themixture under substantially atmospheric pressure, sulphur dioxide andair were introduced continuously thereinto for a period of approximatelythree hours. At the end of this period, the corrosion of the alloy wasessentially complete and the lead, iron, zinc and tin compounds of thealloy existed as sulphates; and the copper and silver compounds existedas sulphides, the iron, zinc and tin compounds being dissolved in thereaction mixture solution andthe other derivatives being in the solidphase.

The degree of subdivision of the metal to be corroded and converted hasa considerable bearing upon the rate of the corrosion reactions,consequently, the times set forth above may be much longer or shorterthan those which may be obained tusing, as starting materials, metals01' alloys of somewhat different piece size. For instance, instead of 24hours being required for complete corrosion of Monal metal, a total of5% orlO hours may be sufiicient if the material is reduced to anextremely fine subdivision condition.

This matter of the condition of the starting material carries over withother facts described above such as acid concentration, temperature andpressure to the practice of the invention as applied! to metal compoundssuch as nickel sulphide-tungsten sulphide.

In an experiment carried out on a laboratory scale, I. treated grams ofthis mixed sulphide material in somewhat comminuted form with aqueoussulphuric acid, bubbling sulphur dioxide gas into the acid solutionwhile the temperature of the solution was maintained at approximately 90C. The sulphuric acid solution was prepared by mixing 49.5 grams of 66B. acid with 100 cc. of water. Air was also bubbled into the solution asdescribed above at about the same rate and in about the same amount asthe sulphur dioxide. Within about six hours, the conversion of thenickel sulphide to nickel sulphate was virtually complete and a goodseparation of tungsten sulphide as a sludge was obtained by decanting 05the liquor and filtering and washing the residue of the reactionmixture.

In a similar experiment on this mixed sulphide material I introduced anacid solution into a reaction vessel of the type described above andcontaining 100 grams of nickel sulphide-tungsten sulphide, this solutioncontaining 75 cc. of hydrochloric acid of 28% strength by weight and 77cc. of water. While maintaining the mixture under substantiallyatmospheric pressure and maintaining the temperature of the mixture atapproximately 90 C.,. I continuously bubbled air and sulphur dioxide gasinto the solution in about equal volumes for a period of three hours. Atthe end oii this time, the reaction ceased due to exhaustion of theacid, and I filtered the liquor from the residue, determining that theliquid phase contained in solution the nickel chloride product, whilethe tungsten sulphide product existed in the form of a sludge andconstituted part of the residue. The separation of the nickel andtungsten values was substantially as sharp as, and yields of reaction ofproducts were substantially as great as those stated in the foregoingexample.

I have furthermore carried out this invention on various metals, metalalloys, and materials containing metals in the form of compounds, withacids of initially comparatively very low strength. It will beunderstood, how ever, that generally operations of this type will not befound very practical or commercial because of the small yields ofdesired products due to the rapid exhaustion of the acid available forreaction.

Nitric acid of about 0.5% strength by weight was tested as generallydescribed above and found to operate successfully, producing detectableamounts of fhe desired metal compounds. In one typical experiment I used250 cc. of an aqueous nitric acid solution of 0.5% strength, adding itto 250 grams. of brass turnings contained in a typical reactor of thetype described above and turning sulphur dioxide gas and air insubstantially equal volumes into the mixture and gassing it for a periodof 30 minutes. The experiment was carried out with the mixture underatmospheric pressure, but the temperature of the mixture was allowed torise from its initial room temperature as exothermic heat was generated.At the end of this period the acid. was substantially exhausted and thereaction virtually ceased, although some. brass was left unreacted. Thezinc of the portion of the brass reacted was found in solution in theform of zinc nitrate, while the copper of that portion was in the formof copper sulphide sludge.

Sulphuric acid likewise proved to be efiiective in this smallconcentration, the experiment being carried out again with 250 grams ofbrass and 250. cc. of 0.5% strength by weight, sulphuric. acid making.up the starting mixture. In this experiment, however, heat was appliedto the mixture and its temperature was raised to 95 to 100 C., prior tothe introduction of the sulphur dioxide gas and air thereinto. Thistemperature was maintained throughout the 30 minute gassing period. Onanalysis, the zinc portion of the brass reacted was in the form of zincsulphate, substantially none of which was found. in solution due to theexhaustion of the acid; and the copper was in the form of coppersulphide sludge.

A solution of 0.5 strength by weight of formic acid was used in thissame way, being applied, however, to Monel metal turnings rather thanbrass, and it was found that the results obtained corresponded to thosedescribed in the above examples. Nickel formate was formed in relativelysmall amount, but. in proportion tothe quantity of acid used, during the30 minute reaction period; and the copper was converted to sulphide andcollected as a sludge. The temperature and pressure conditions weresubstantially as defined above in connection with the discussion of theexperiment on the 0.5 sulphuric acid solution.

Acetic acid likewise proved to be effective in this very small initialconcentration as determined in an experiment carried out as describedabove with reference to this 0.5% sulphuric acid solution. Monel metalwas used in this operation and nickel'acetate and copper sulphide werethe reaction products. The temperature and pressure conditions were thesame as those in the said sulphuric acid test.

In still another experiment, hydrofluoric acid was found to be effectivein this very low initial concentration zinc fluoride and copper sulphidewere formed, brass being; used instead of Monel metal. Again, thetemperature and pressure circumstances were those described in the saidsulphuric acid experiment.

A solution (250' cc.) of 0.5% strength by weight of hydrochloric acidwas gassed with sulphur dioxide for 30- minutes, the solutiontemperature being maintained between about 80. C. and about 100 C. Monelmetal turnings (250- grams) mixed in the. solution prior to the gassingwere corroded appreciably and nickel chloride and copper. sulphide wereformed in. appreciable amounts, the nickel salt being dissolved in theliquid phase of the reaction mixture and the copper sulphide existing asa. slude-Like accumulation on the bottom of the reactor. The acid wasessentially exhausted at the end of the gassing period and the. metalcorrosion reactions had apparently ceased by that time- Phosphoric.acid: was used in. this same manner and found to be efifective in lowconcentration. A solution (250 cc.) of phosphoric acid of 0.5 strengthby weight was poured into a reactor of the type described above,.containing 250 grams of brass turnings and the resulting mixture washeated to about 95 C. Sulphur dioxide gas was. then bubbled into thesolution continuously for a period of about 30 minutes, at the end ofwhich time the reactions. appeared to. have ceased and the acid contentof the mitxurewas. substantially exhausted. Zinc phosphate and coppersulphide produced in the reaction mixture through the metal corrosionreactions going on during the. gassing; period were separated togetheras a sludge from the. liquid phase of the said reaction mixture.

In order tov determine. the applicability of this process. of myinvention to metals standing below hydrogen in this series, I carriedout several experiments described below using various of the acids setforth above and employing; sulphur dioxide in all instances and air incertain cases and. imposing, pressure on the reaction mixture during thereact-ion period in one instance.

Using finely-divided antimony metal and a 25% sulphuric acid solution, Icontacted sulphur dioxide with the metal in the acid solution. in themanner described above, continuously running the sulphur dioxide gasinto the bottom of the vessel, while maintaining the temperature of thegas mixture throughout substantially the entire reaction period atapproximately C. and maintaining the pressure at approximatelyatmospheric. The reaction. appeared. to go to completion and exhaustionof the available antimony metal in a matter of about four and one-halfhours, approximately 80 grams of metal having been charged initially.The antimony was converted in this reaction to the sulphide whichcollected on the bottom of the reaction vessel as a sludge-like massvwhich was easily separated from the mixture by filtration.

In a similar test I used copper in finely-divided form, introducing. itinto a solution of hydrochloric acid of about 28% strength. and dilutedto about four times its volume with pure water. The available coppercharged to the mixture this way was substantially completely convertedto: copper sulphide in about six and one-half hours, during. which timesulphur dioxide was continuously introduced into the mixture and thetemperature of the mixture. was maintained at approximately C. Thecopper sulphide was collected as a sludge which settled from the. liquidphase of the mixture and was readily separated therefrom.

In a similar test using tungsten in finely-divided form. and phosphoricacid, I produced tungsten sulphide as a sludge-like product whichcollected on the bottom of the.

vessel. Substantially complete exhaustion of the mixture of availabletungsten metal in about five and one-half hours, during which timesulphur dioxide and air in equal volumes. were bubbled into the bottomof the reaction vessel. The phosphoric acid solution was prepared asdescribed above, 125 cc. of 85% orthophosphoric acid being diluted with250 cc. of water and 400 grams of tungsten was charged into theresulting solution to make the starting mixture.

Molybdenum sulphide was produced in a similar experiment, the corrosionreaction proceeding rapidly in an acetic acid solution prepared bydiluting 200 cc. of commercial glacial acid with 200 cc. of water. Intothe resulting acid solution 400 grams of molybdenum metal infinely-divided form was charged. The reactionperiod was five andone-half hours, during which time sulphur dioxide and air wereintroduced continuously at the rate of one bubble per second in eachinstance. However, throughout this reaction period, a pressure of 30lbs. per square inch gauge was maintained on the reaction mixture. Closeobservation of the reaction, however, indicated that the reaction didnot proceed any more rapidly in this case than in any of the foregoingwhere atmospheric pressure was applied throughout the period to thereaction mixture.

In still another test, I have successfully used nitric acid to ettectthe corrosion of antimony metal to produce the result and advantages ofthis invention stated above. In this test, approximately 400 grams ofantimony was charged into nitric acid diluted to about strength andsulphur dioxide and air were bubbled continuously into the resultingreaction mixture at a rate of about one bubble per second. The corrosionof the antimony and the production of antimony sulphide proceeded at arelatively rapid rate until substantially all the available antimonymetal was converted in a matter of about four and one-half hours. Theantimony sulphide accumulated on the bottom of the vessel as asludge-like mass and was easily separated from the reaction mixture.

To test the effectiveness of the method of this invention as applied toa physical mixture consisting of metals below hydrogen in the series, Iemployed finely-divided copper metal and antimony metal, introducingthese metals into a solution of hydrochloric acid of about 28% strengthdiluted to about four times its volume with pure water. The availablecopper and antimony charged to the mixture were substantially completelyconverted to the respective sulphides in about six and one-half hours,during which time sulphur dioxide was continuously bubbled into themixture and the temperature of the mixture was maintained atapproximately 90 C. The copper sulphide and antimony sulphide werecollected as a sludge which settled from the liquid phase of the mixtureand was easily separated therefrom.

Nitric acid of about 5.0% strength by weight was tested as generallydescribed above and found to operate successfully producing detectableamounts of the desired metal compounds. In one typical experiment, Iused 250 cc. of an aqueous nitric acid solution of 5.0% strength, addingit to 250 grams of a physical mixture of zinc and copper contained in atypical reactor of the type described above and turning sulphur dioxidegas and air in substantially equal volumes into the mixture and gassingit for a period of thirty minutes. The experiment was carried out withthe mixture under atmospheric pressure, but the temperature of themixture was allowed to rise from its initial room temperature asexothermic heat was generated. At the end of this period, the acid wassubstantially exhausted and the reaction virtually ceased, although someof the metal mixture was left unreacted. The zinc of the portion of themetal mixture reacted was found in solution in the form of zinc nitrate,while the copper of that portion was in the form of copper sulphidesludge.

Sulphuric acid likewise proved to be effective in this smallconcentration, the experiment being carried out again with 250 grams ofa physical mixture of copper and zinc and 250 cc. of 5.0% strength byweight, sulphuric acid making up the starting mixture. In thisexperiment,

however, heat was applied to the mixture and its temperature was raisedto 95 to 100 C., prior to the introduction of the sulphur dioxide gasand air thereinto. This temperature was maintained throughout the thirtyminutes gassing period. On analysis, the zinc portion of the metalmixture reacted was in the form of zinc sulphate in solution; and thecopper was in the form of copper sulphide sludge.

A solution of 5.0% strength by weight of formic acid was used in thissame way, being applied, however, to a nickel-copper mixture rather thanto a physical mixture of copper and zinc, and it was found that theresults obtained corresponded to those described in the above examples.Nickel for-mate was formed in relatively small amount, but in proportionto the quantity of acid used, during the thirty minute reaction period;and the copper was converted to sulphide and collected as a sludge. Thetemperature and pressure conditions were substantially as defined abovein connection with the dis cussion of the experiment on the 5.0%sulphuric acid solution.

Acetic acid likewise proved to be eflfected in this very small initialconcentration as determined in an experiment carried out as describedabove with reference to this 5.0% sulphuric acid solution. Anickel-copper mixture was used in this operation and nickel acetate andcopper sulphide were the reaction products. The temperature and pressureconditions were the same as those in the said sulphuric acid test.

In still another experiment, hydrofluoric acid was found to be effectivein this very low initial concentration and zinc fluoride and coppersulphide were formed, a physical mixture of zinc and copper being usedinstead. Again, the temperature and pressure circumstances were thosedescribed in the said sulphuric acid experiment.

A solution (250 cc.) of 5.0% strength by weight of hydrochloric acid wasgassed with sulphur dioxide for thirty minutes, the solution temperaturebeing maintained between about C. and about 100 C. A physical mixturesof nickel and copper (250 grams) added to the solution prior to thegassing were corroded substantially and nickel chloride and coppersulphide were formed in appreciable amounts, the nickel salt beingdissolved in the liquid phase of the reaction mixture and the coppersulphide existing as a sludge-like accumulation on the bottom of thereactor. The acid was essentially exhausted at the end of the gassingperiod and the metal corrosion reactions had apparently ceased by thattime.

Phosphoric acid was used in this same manner and found to be effectivein low concentration. A solution (250 cc.) of phosphoric acid of 5.0%strength by weight was poured into a reactor of the type describedabove, containing 250 grams at a physical mixture of copper and zinc andthe resulting mixture was heated to about C. Sulphur dioxide gas wasthen bubbled into the solution continuously for a period of about thirtyminutes, at the end of which time the reactions appeared to have ceasedand the acid content of the mixture was substantially exhausted. Zincphosphate and copper sulphide produced in the reaction mixture throughthe metal corrosion reactions going on during the gassing period wereseparated together as a sludge from the liquid phase of the saidreaction mixture.

In each of the foregoing examples where the initial acid concentrationof the reaction mixture amounted to approximately 5%, a test performedat the end of the reaction period showed in every instance that the acidconcentration at the time that the reactions of this inventionapparently ceased was approximately 0.5%, indicating the criticality ofthis minimum acid value in reaction mixtures of this invention, as setout above.

Since, as stated above, this invention is based upon my discovery thatcertain desirable reactions take place and certain valuable products areobtained when various particular materials are brought together underfavorable circumstances, the important thing is to have the saidmaterials together for as long as necessary to permit the said reactionsto go forward. The manner of bringing the materials together or theorder of their addition to a reaction vessel or a reaction medium thuswill be generally of incidental importance.

This is a continuation-in-part of my copending application, Serial No.332,553, filed January 21, 1953.

Having thus described the present invention so that. others skilled inthe art may understand the same, I state that what I desire to obtain byLetters Patent is set out in whatis claimed.

What is claimed is:

l. The method of rapidly and economically converting a corrosionresistant alloy of at least one metal above and at least one metal belowhydrogen in the electromotive force series into metal compounds whichcomprises the steps of introducing a corrosion resistant alloycontaining said metals into an aqueous solution containing in excess ofabout 0.5% by weight of an acid selected from the group consisting offormic acid, acetic acid, sulphuric acid, hydrofluoric acid, nitricacid, hydrochloric acid, phosphoric acid, and passing sulphur dioxideinto the solution, whereby the insoluble sulphides are precipitated andthe soluble salts of the acid selected are retained in the solution.

2. The method of economically converting a corrosion resistant alloy ofat least one metal above and at least one metal below'hydrogen in theelectromotive force series into metal compounds which comprises thesteps of introducing said alloy into a solution containing in excess ofabout 0.5% by weight of an acid selected from the group consisting offormic acid, acetic acid,

sulphuric acid, hydrofluoric acid, nitric acid, hydrochloric acid andphosphoric acid, at a temperature between about 80 C. and 100 C. andpassing sulphur dioxide into the solution, whereby the insolublesulphides are precipitated and the soluble salts of the acid selectedare retained in the solution.

3. The method of rapidly and economically converting a corrosionresistant alloy of at least one metal above and at least one metal belowhydrogen in the electromotive force series into metal compounds whichcomprises the steps of introducing said alloy into an aqueous solutioncontaining in excess of about 0.5% by weight of an acid selected fromthe group consisting of formic acid, acetic acid, sulphuric acid,hydrofluoric acid, nitric acid, hydrochloric acid, and phosphoric acid,passing r sulphur dioxide into the solution and simultaneously bubblingair into said solution whereby the insoluble sulphides are precipitatedand the soluble salts of the acid selected are retained in the solution.

4. The method of rapidly and economically converting a corrosionresistant alloy of at least one metal above and at least one metal belowhydrogen in the electromotive force series into metal compounds whichcomprises the steps of introducing said alloy into an aqueous solutioncontaining in excess of about 0.5 by weight of an acid selected from thegroup consisting of formic acid, acetic acid, sulphuric acid,hydrofluoric acid, nitricacid, hydrochloric acid and phosphoric acid, ata temperature between about 80 and 100 C. passing sulphur dioxide intothe solution and simultaneously bubbling air into said solution, wherebythe insoluble sulphides are precipitated and the soluble salts of theacid selected are retained in the solution.

5. The method of preparing metal compounds from a corrosion resistantalloy of a metal above and a metal below hydrogen in the electromotiveforce series which comprises introducing the alloy into a solution of atleast 0.5% by weight of an acid selected from the group consisting offormic acid, acetic acid, sulphuric acid, hy-

18 drofluoric acid, nitric acid, hydrochloric acid, and introducingsulphur dioxide into the solution.

6. The method of rapidly, economically and sharply separating values ofmetal above hydrogen in the electromotive force series from values ofanother metal below hydrogen in said series which comprises the steps ofintroducing a corrosion resistant alloy containing said metals into anaqueous solution containing in excess of about 0.5% by weight of anacid, selected from the group consisting of formic acid, acetic acid,sulphuric acid, hydrofluoric acid, hydrochloric acid, nitric acid andphosphoric acid, and passing sulphur dioxide into the solution therebyforming a soluble salt of the selected acid of a metal above hydrogenand an insoluble sulphide of a metal below hydrogen and separating andremoving the sulphide as a solid from the liquid phase of the reactionmixture containing said soluble salt.

7. The method of preparing metal compounds from an alloy which consistsin introducing into a solution of at least 0.5 by weight of sulphuricacid an alloy which is normally very resistant to corrosion by saidsolution, passing sulphur dioxide into the solution and reducing saidsulphur dioxide until a major part of the alloy has been converted intometal compounds, and recovering the resulting compounds from thereaction mixture.

8. A method of preparing metal compounds from corrosion resistant alloysof at least one metal above and at least one metal below hydrogen in theelectromotive force series which consists in introducing the alloy intoa solution at a temperature between about C. and C. containing at least0.5 by weight of hydrochloric acid and passing sulphur dioxide into thesolution thereby giving a solution of a soluble chloride and aprecipitate of the insoluble sulphide.

9. The method of preparing metal compounds from corrosion resistantalloy of at least one metal above and at least one metal below hydrogenin the electromotive force series which consists in introducing thealloy into a solution at substantially room temperature and containingat least 0.5 by weight of nitric acid, passing sulphur dioxide into thesolution and simultaneously bubbling air into said solution, the sulphurdioxide and air being delivered into the solution in substantially equalvolumes and at substantially the same rate, thereby giving a solution ofa soluble nitrate and a precipitate of the insoluble sulphide.

10. A process for the manufacture of nickel sulphate and copper sulphidefrom a nickel copper alloy which comprises introducing said alloy into acontinuously bubbling aqueous sulphuric acid bath containing at least0.5% by weight of sulphuric acid, and passing sulphur dioxide into saidbath and into contact with said alloy,-

whereby copper sulphide is precipitated and nickel sulphate obtained inthe solution.

11. In the process set forth in claim 10, delivering air continuouslyinto the said bath simultaneously with the sulphur dioxide.

12. The method of rapidly, economically and sharply separating thecopper values from the nickel values of Monel metal which comprises thesteps of heating an aqueous sulphuric acid solution containing at least0.5 sulphuric acid in contact with said Monel metal, bringing sulphurdioxide into said solution and forming copper sulphide and nickelsulphate, and separating and removing said copper sulphide as a solidfrom the reaction mixture.

13. The process for the manufacture of nickel sulphate and coppersulphide from a nickel copper alloy which comprises subjecting the saidalloy, in a discrete condition, to a continuously boiling bath of asulphuric acid dissolved in water, in the approximate proportion of 30%of acid by volume to water, delivering sulphur dioxide continuously intosaid bath and into contact with the said alloy therein, maintainingsubstantially constant the volume of the bath by addition thereto ofWater to compensate for the loss of water due to the boiling of the 19bath, continuing the boiling of the bath until the sulphuric acidtherein is substantially exhausted, and separately recovering theresulting nickel sulphate solution and the insoluble copper sulphide.

14. The process for the manufacture of nickel sulphate and coppersulphide from a nickel-copper alloy comprises subjecting the said alloy,in a discrete condition, to a continuously boiling bath of sulphuricacid dissolved in water, the approximate proportion of acid to waterbeing 30% by volume, a portion of the acid being incorporated in thebath at the beginning of the operation and the remainder of the acidbeing added to the bath when the proportion of acid to the bath shallhave fallen to a predetermined degree, delivering sulphur dioxidecontinuously into said bath and into contact with the said alloytherein, maintaining substantially constant the volume of the bath byaddition thereto of water to compensate for the loss of water due to theboiling of the bath, continuing the boiling of the bath until thesulphuric acid therein is substantially exhausted, and separatelyrecovering the resulting nickel, sulphate solution and the insolublecopper sulphide.

15. That method of forming nickel sulphate and copper sulphide from anickel-copper alloy comprising the steps of preparing an aqueousreaction bath of concentrated sulphuric acid, associating the alloy withthe bath, heating the bath to approximately its boiling temperaturewhile the bath is retained under'atmospheric pressure, maintaining thevolume of the bath substantially uniform by adding water thereto atintermittent intervals, adding an additional volume of concentratedsulphuric acid to the bath after the original acid composition of thebath has been reduced by reaction of the acid, continuously passingsulphur dioxide into the bathand into contact with the alloy tosulphurize the copper and form insoluble copper sulphide therefrom,continuously passing air into the bath simultaneously with the sulphurdioxide to also contact the alloy therein, oxidizing the nickel of thealloy to form a solution of nickel sulphate therefrom, filtering thebath to obtain the copper sulphide therefrom, and thereafter recoveringnickel sulphate from the filtrate.

16. A process for the manufacture of a cobalt salt and copper sulphidefrom a cobalt-copper alloy which comprises introducing said alloy intoan aqueous solution containing an excess of about 0.5% by weight of anacid selected from the group consisting of formic acid, acetic acid,sulphuric acid, hydrofluoric acid, hydrochloric acid, nitric acid, andphosphoric acid, and passing sulphur dioxide into the solution andthereby forming a soluble cobalt salt of the selected acid and coppersulphide.

17. The method of rapidly and economically converting a metal into acompound of said metal, which comprises the steps of introducing into anaqueous solution containing in excess of about .5% by weight of a strongacid a metal which is normally very resistant to corrosion by saidsolution, passing therein sulphur dioxide and reducing the sulphurdioxide until the major part of the metal has been converted into ametal compound, and recovering the resulting compound from the reactionmixture.

18. A process as claimed in claim 17 wherein the aqueous solution of theacid is maintained at a temperature of about 80 C. to 100 C.

19. A process as claimed in claim 17 wherein air is simultaneouslyintroduced into the solution with the sulphur dioxide.

20. A method of rapidly and economically converting metals standingabove hydrogen in the electromotive series into a solution of said metalsalts, which comprises the steps of introducing into an aqueous solutioncontaining in excess of about .5% by weight of a strong acid metalsstanding above hydrogen in said series and normally very resistant tocorrosion by said solution, introducing therein sulphur dioxide andreducing said sulphur dioxide in said solution until the major parts ofthe metals have been converted into metal salts, and recovering theresulting salts from the reaction mixture.

21. A method of rapidly and economically converting metallic cobalt intocobalt sulphate solution, whichcomprises the steps of introducing saidcobalt into an aqueous.

weight of a strong acid and introducing therein sulphur' dioxide,reducing the sulphur dioxide and producing elemental sulphur.

24. A method of rapidly and economically converting metallic cobalt intoa solution of the salt, which comprises the steps of introducing saidcobalt into an aqueous solution containing in excess of about .5% byweight of a strong acid and introducing therein sulphur dioxide,reducing the sulphur dioxide and producing elemental sulphur.

25. A method of preparing a nickel salt solution from metallic nickel,which consists in introducing said nickel into a solution of at least.5% by weight of a strong acid and introducing sulphur dioxide into thesolution, reducing the sulphur dioxide and precipitating elementalsulphur.

26. The method of rapidly and economically converting metals standingbelow hydrogen in the electromotive series into a mixture of metalsulphides, which comprises the steps of introducing into an aqueoussolution containing in excess of about .5 by weight of a strong acidmetals standing below hydrogen in said series and normally veryresistant to corrosion by said solution and running a stream of sulphurdioxide gas into said solution, reducing the sulphur dioxide andprecipitating the insoluble sulphides.

27. The method of rapidly and economically converting a metal into acompound of said metal, which comprises the steps of introducing into anaqueous solution containing about 5% by weight of a strong acid a metalwhich is normally very resistant to corrosion by said solution, passingtherein sulphur dioxide and reducing the sulphur dioxide until the majorpart of the metal has been converted to a metal compound, and recoveringthe resulting compound from the reaction mixture.

28. The method of rapidly and economically converting metals standingabove hydrogen in the electromotive series into a solution of salts ofsaid metals, which comprises the steps of introducing into an aqueoussolution containing about 5% by weight of a strong acid metals standingabove hydrogen in said series and normally very resistant to corrosionby said solution and introducing therein sulphur dioxide and reducingthe sulphur dioxide until the major parts of the metals have beenconverted into salts of the metals, and recovering the resulting saltsfrom the reaction mixture.

29. The method of rapidly and economically converting metals standingbelow hydrogen in the electromotive series into a mixture of metalsulphides, which comprises the steps of introducing into an aqueoussolution containing 5% by weight of a strong acid metals standing belowhydrogen in said series and normally very resistant to corrosion by saidsolution, running a stream of sulphur dioxide gas into said solution,reducing the sulphur dioxide and precipitating the insoluble sulphides.

30. The method of preparing metal compounds from a corrosion resistantalloy of a metal above and a metal below hydrogen in the electromotiveforce series which comprises introducing the alloy into a solution of 5%by weight of an acid selected from the group consisting of formic acid,acetic acid, sulphuric acid, hydrofluoric acid, nitric acid,hydrochloric acid and phosphoric acid, and introducing sulphur dioxideinto the solution.

31. A process for the manufacture of nickel sulphate and copper sulphidefrom a nickel copper alloy which comprises introducing said alloy into acontinuously bubbling aqueous sulphuric acid bath containing 5% byweight of sulphuric acid, and passing sulphur dioxide into said bath andinto contact with said alloy, whereby copper sulphide is precipitatedand nickel sulphate is obtained in the solution.

32. The method of rapidly and economically converting a nickel-chromiumalloy into a solution of salts of nickel and chromium, which comprisesthe steps of introducing the said alloy into an aqueous solutioncontaining about 5% by weight of a strong acid, introducing sulphurdioxide into said solution, reducing the sulphur dioxide and producingelemental sulphur.

No references cited.

1. THE METHOD OF RAPIDLY AND ECONOMICALLY CONVERTING A CORROSIONRESISTANT ALLOY OF AT LEAST ONE METAL ABOVE AND AT LEAST ONE METAL BELOWHYDROGEN IN THE ELECTROMOTIVE FORCE SERIES INTO METAL COMPOUNDS WHICHCOMPRISES THE STEPS OF INTRODUCING A CORROSION RESISTANT ALLOYCONTAINING SAID METALS INTO AN AQUEOUS SOLUTION CONTAINING IN EXCESS OFABOUT 0.5% BY WEIGHT OF AN ACID SELECTED FROM THE GROUP CONSISTING OFFORMIC ACID, ACETIC ACID, SULPHURIC ACID, HYDROFLUORIC ACID, NITRICACID, HYDROCHLORIC ACID, PHOSPHORIC ACID, AND PASSING SULPHUR DIOXIDEINTO THE SOLUTION, WHEREBY THE INSOLUBLE SULPHIDES ARE PRECIPITATED ANDTHE SOLUBLE SALTS OF THE ACID SELECTED ARE RETAINED IN THE SOLUTION.